I posted my original problems in the below thread. Turned out that a major part of the problem was no ground on the headlight switch. Seemed to take care of 90% of the problems. Still having problems with the left rear tail light. Turn signal works with lights off. With lights on, left turnsignal causes left rear tail light to go out. Same with brakes. No problem with the right tail light.

Seems strange, cause the taillights run from the headlight switch to the left side, then from left to the right.

Also noticed left turn signal seems slow when its working and left tail light is dimmer than the right.

Have changed bulbs, new housing, grounded bed to frame. Amy thoughts?

https://www.ford-trucks.com/forums/8...-troubles.html

 

Do you have a ground strap running from the frame to the cab? The frame is not grounded automatically because the engine mounts in rubber. In most cases there is a ground strap from the block to the firewall, which grounds the cab. A separate ground strap grounds the cab to the frame. These are important.

By "housing" do you mean the bulb socket?

 

Yes,
Cab is grounded to the frame. The Bed is grounded to the frame. When I say tail light housing, I mean the complete assembly is new including bulb sockets. It is bolted to the bed which is grounded to the frame.

 

It's most likely your turn signal switch.

 

Brand new switch.

 

It sounds like a ground issue in the socket itself. Use a multimeter to ohm out the tail light socket ground against the bed.

 

Where did you get it from, some after market TSS leave much to be desired, SHEE-MAR switches out of CO. are factory duplicates and better than the cheaper stuff.

 

Yeah FMC. I'm thinking a ground issue too. I will double check the ground on the tail light housing (scoket). But the old one did exactly the same thing.

Montana Highboy, I bought the switch from National Parts Depot. Anything is possible, but everything elese is working perfectly.

Th light cutting out when additional power goes to it is what gets me. Almost like its shorting out.

 

Usually, when one light coming on causes another light to go out, it's a ground problem. The lights are on two different circuits, but share the same ground. When there is unwanted resistance in the ground path, this resistance creates a voltage drop that takes away from the available voltage that can drop across the bulbs. Ideally you want all 12 volts to drop across the bulb, but if there is resistance in the ground path, some drops across the bulb filament, and the remainder drops across the ground path resistance. With just the headlights on, only one filament in the bulb is lit. The ground path resistance is in series with the bulb filament, so the current flowing through the bulb filament also flows through the ground path resistance, creating a voltage drop across the ground path resistance. This takes away from the voltage available to the bulb, but there's still enough voltage for the bulb to emit light. However, when the turn signal comes on, an extra filament draws current, which increases the voltage across the ground resistance and can be enough to dim the bulbs or put them out. This is called ground shift. It earns its name because the ground at the bulb filament "shifts" away from the electrical system's true ground. A resistance check will confirm or deny this conclusion. Note that this can only be tested electrically (with a multimeter); inspecting the sockets visually will not yield any conclusive information.

 

Thanks FMC. Look like I've got my homework for tomorrow.

 

FMC,
Spent a half hour with a dremel tool cleaning up powder coat from all the bolt holes in the tail light assembley bracket. Then I chased all of the threaded bolt holes, and shazam. All the lighting works. Hopefully now I can start buttoning it all up. Thanks FMC400 and Montana Highboy for the ideas.

 

Awesome! Glad to hear you're up and running.

 

I kinda had the same problem with my tail lights when I got them all hooked up. I had the entire underneath of the bed rhinolined so I lost all the ground from the bed. So, I just ran ground wire from my tail lights to the chassis and shazzam, good to go.